Diffusion of smoke-free policies at outdoor sports clubs in the Netherlands

Background Although outdoor smoke-free policies (SFPs) at sports clubs represent an important new area of tobacco control, the majority of sports clubs are not smoke free. This study aims to assess diffusion patterns of outdoor SFPs at sports clubs in the Netherlands. Methods Using a retrospective, registry-based design, an inventory was made of football, field hockey, tennis and korfball clubs that became smoke free between 2016 and 2020. We determined the type of sports, number of members and proportion of youth members. The degree of urbanisation and density of smoke-free sports clubs were measured at the municipality level. The association between sports clubs’ characteristics, degree of urbanisation and SFP adoption was analysed using multilevel regression analysis. Horizontal diffusion was tested by analysing the association between the density and annual incidence of smoke-free sports clubs. Results Since 2016, the number of sports clubs with an outdoor SFP increased from 0.3% to 26.4%. Field hockey and korfball clubs and clubs with many (youth) members were more likely to be smoke-free. SFPs spread from the most urbanised to less urbanised municipalities, which could mostly be attributed to sports clubs’ characteristics. A higher density of smoke-free sports clubs within municipalities was associated with an increased incidence of new SFPs in the following year. Conclusion Outdoor SFPs at sports clubs in the Netherlands diffused across horizontal and hierarchical lines. National strategies for smoke-free sports should monitor clubs that are more likely to stay behind, such as football and tennis clubs, smaller clubs and clubs in less urbanised areas.


INTRODUCTION
Nowadays, 28% of the European and 14.8% of the Dutch adult population still smokes daily. 1 Therefore, reducing the number of smokers is an urgent theme in several (inter)national public health agreements. In the Netherlands, the government has agreed on a number of measures in the National Prevention Agreement (NPA) to realise a 'smokefree generation' by 2040 and to reduce smoking prevalence to <5% among adults and to 0% among youth and pregnant women. 2 One of the key components of strategies to attain a smoke-free generation is the implementation of smoke-free policies (SFPs). SFPs have proven to be effective at protecting children from secondhand smoke (SHS) and its adverse health consequences. 3 Furthermore, SFPs have been associated with smoking cessation, reduced tobacco use, reduced likelihood of smoking initiation among youth and denormalisation of smoking. [4][5][6][7] SFPs have been widely implemented, and initially they focused on restricting smoking at certain indoor locations. 8 In more recent years, SFPs have been implemented that ban smoking in outdoor public places such as parks, playgrounds and outdoor sports clubs. 8 The latter has great potential to reduce exposure of youth to SHS as sports clubs are often visited by children when they grow up. 9 For example, 74% of Dutch children aged 6-11 years are member of a sports club. 10 According to one of the goals in the NPA, all Dutch sports clubs are expected to be smoke free by 2025. A smoke-free sports club means that smoking is no longer allowed on the sports club's venue or that agreements have been made to ensure that children are no longer exposed to smoking. 2 A recent study found that key stakeholders at sports clubs perceived the implementation of an outdoor SFP as feasible. 11 Moreover, support for an outdoor SFP at sports clubs is high, as most people believe there is a need to protect children from SHS and that sports and smoking do not fit together. 12 Despite of this support, sports clubs may refrain from adopting an outdoor SFP for several reasons. For example, an outdoor SFP might affect the social functioning of the club, its enforcement might cause problems and an SFP may not be given priority due to the sport clubs' many other concerns. 12 In order to achieve the goal of 'all sports clubs smoke-free by 2025', it is important to gain insight into how outdoor SFPs at sports clubs diffuse across the Netherlands.
Policy diffusion can be analysed in several ways. According to Rogers' diffusion of innovations theory, an innovation (a new product, idea or initiative) spreads over time across horizontal networks, that is, the diffusion follows borders of geographical areas. 13 Besides horizontally, policies can also diffuse hierarchically, 14 15 with larger cities and more urbanised regions being the point of initiation, followed by smaller towns and then more rural regions.
Several studies have investigated the diffusion of SFPs. A study in Indonesia found a horizontal diffusion pattern: districts were more likely to adopt an SFP if adjacent districts did so as well. 16 Districts were less likely to adopt an SFP if adoption already took place on the provincial level, indicating that the adoption of SFPs did not follow a hierarchical diffusion pattern. A Canadian study found that adoption of smoke-free bylaws followed both hierarchical and horizontal diffusion patterns: adoption was initiated by larger cities and subsequently expanded out to nearby smaller cities, indicating that urban hierarchy as well as the proximity between adopters were influencing the adoption of smoke free by laws. 15

Original research
To date, the diffusion of SFPs among outdoor sports clubs has not been studied. Understanding this diffusion pattern and the characteristics that are associated with adoption may inform policies aimed at making all outdoor sports clubs smoke free. Therefore, the current study aims to assess whether the adoption of outdoor SFPs at Dutch sports clubs follows patterns of horizontal diffusion or hierarchical diffusion and whether these patterns are related to specific characteristics of outdoor sports clubs.

Study design and population
This study used a retrospective study design based on a continuous registry of SFPs among sports clubs. The study population consisted of all football, tennis, korfball and field hockey clubs in the Netherlands. In terms of membership numbers, these are the most popular outdoor sports among Dutch children. 17 A total of 4825 sports clubs were included in the study.
In the Netherlands, sports clubs are mainly organised on a national level, under an umbrella organisation (NOC*NSF (Nederlands Olympisch Commité * Nederlandse Sport Federatie)) to which 90 national sports organisations and almost 24 000 sports clubs are affiliated. The NPA stipulated that NOC*NSF, together with the affiliated sports federations, would encourage sports clubs to become smoke free by 2025. 2 Currently, there is no national legislation that prohibits or restricts outdoor smoking at sports clubs. However, municipalities may encourage SFP adoption. Since sports accommodations are often built on municipality terrains, they could include the obligation to introduce an outdoor SFP when granting of subsidies for sports clubs. In addition, municipalities could designate smoke-free zones within their municipality, although this is not yet common practice.

Data collection
In February 2021, data were obtained from various sources. Information on characteristics of the sports clubs (eg, type of sports and postal code) was provided by NOC*NSF, 18 which has an up-to-date overview of all sports clubs in the Netherlands. The total number of members and the number of youth members were provided by the national sports federations. Documentation on sports clubs with an outdoor SFP was provided by the Dutch Heart Foundation, 19 which keeps track of clubs that have ordered smoke-free materials used to indicate that their sports club is smoke free. This register also contains information about the year of implementation of the outdoor SFP. There are no specific criteria for sports clubs to be registered as smoke free. That is, sports clubs can decide themselves when/where/to whom the SFP applies and how the policy is communicated and enforced. If the total number of members and/or the number of youth members was not known by the sports federations or the year of implementation was missing in the register of the Dutch Heart Foundation, the sports club was contacted by email or via social media to provide this information themselves. Sports clubs for which we could not determine their membership numbers (n=27) or the implementation year of the outdoor SFP (n=26) were excluded from the relevant analyses.

Outcome variables
The first outcome variable was the point prevalence of smokefree sports clubs on 31 December of each year between 2016 and 2020. Whether or not a sports club had an outdoor SFP was dichotomised as 0=no and 1=yes. The point prevalence was used as an outcome variable when analysing whether the adoption of an outdoor SFP was associated with sports clubs' characteristics and the degree of urbanisation.
The second outcome variable was the annual incidence of smoke-free sports clubs. Whether a sports clubs had adopted an outdoor SFP during a particular year between 2016 and 2020 was dichotomised as 0=no and 1=yes for each of these 5 years. The annual incidence was used as an outcome variable when analysing whether the adoption of an outdoor SFP in a particular year was associated with the density of smoke-free sports clubs within the corresponding municipality at the start of that year.

Independent variables
We determined three characteristics of sports clubs: type of sports, total number of members and proportion of youth members (club members under the age of 18 years). The continuous variables 'total number of members' and 'proportion of youth members' were divided into five quintiles to create equally distributed groups.
In addition, we determined the degree of urbanisation of the municipality to which the sports club belonged using publicly accessible data. 20 The degree of urbanisation was measured at municipality level, since neighbourhood level was considered too narrow (in 2016, the Netherlands had 380 municipalities, with an average of 43 667 citizens per municipality). The degree of urbanisation was based on the address density of the municipality and included five categories: not urbanised (<500 addresses per km 2 ), hardly urbanised (500-1000 addresses per km 2 ), moderately urbanised (1000-1500 addresses per km 2 ), strongly urbanised (1500-2500 addresses per km 2 ) and most urbanised (>2500 addresses per km 2 ).
We also measured the density of smoke-free sports clubs within a municipality, by dividing the number of smoke-free sports clubs in a municipality by the total number of sports clubs in that municipality. The density of smoke-free sports clubs within a municipality was measured at, respectively, 31 December of 2017, 2018 and 2019. For each time, it was classified into six categories (0%, 1%-20%, 21%-40%, 41%-60%, 61%-80% and 81%-100%).

Data analysis
Data were analysed using SPSS Statistics, V.26.0. 21 First, the point prevalence and annual incidence of smoke-free sports clubs were computed for each year between 2016 and 2020. Second, the point prevalence of smoke-free sports clubs at 31 December 2020, was computed according to characteristics of sports clubs and degree of urbanisation. Third, a multilevel logistic regression analysis was used to analyse the association between sports clubs' characteristics, the degree of urbanisation and the point prevalence of smoke-free sports clubs at 31 December 2020. Finally, a similar regression model was used to analyse the association between the density of smoke-free sports clubs within a municipality and the annual incidence of smoke-free sports. The latter two analyses were performed using both univariate and multivariate analyses to assess the extent to which observed patterns of diffusion could be attributed to specific club characteristics.
Multilevel analyses were carried out to take into account potential clustering within the data, since sports clubs (level 1) are nested in municipalities (level 2). For both analyses, an intercept-only model concluded that the variance in the intercepts was significantly different from zero (p<0.001), thus providing evidence for clustering within the data. For example, for the prevalence of SFP in 2020, the intraclass correlation coefficient was calculated at 0.17, indicating that 17% of the variation between clubs can be attributed to clustering within municipalities. For all analyses, a significance level of p<0.05 was used.

Characteristics of the study population
Half of the included sports clubs were football clubs (n=2388, 49.5%), followed by tennis (n=1662, 34.4%), field hockey (n=452, 9.4%) and korfball (n=323, 6.7%) clubs. Descriptive analyses of the included sports clubs are presented in appendices I and II. Table 1 presents the point prevalence and annual incidence of sports clubs with an outdoor SFP at five moments in time. Between January 2016 and December 2020, 1273 out of 4825 sports clubs (26.4%) adopted an outdoor SFP, of which 26 clubs (0.5%) had an unknown implementation year. In 2016, only 13 sports clubs (0.3% of all sports clubs) adopted an outdoor SFP. A strong upward trend in the percentage of smoke-free sports clubs can be observed from 2018 on. The largest increase in smokefree sports clubs occurred in 2019, with 507 clubs becoming smoke free, accounting for 40.7% of all smoke-free sports clubs. Table 2 presents the prevalence of SFPs according to characteristics of sports clubs and the degree of urbanisation. Whereas football clubs accounted for the highest number of SFP adoptions (n=614, 25.7%), field hockey clubs had the highest prevalence of SFP adoption (n=232, 71.8%). SFP adoption substantially differed between sports clubs with less than 120 members (9.4%) and sports clubs with over 548 members (48.9%). Similarly, of the sports clubs with less than 14.5% youth members, only 8.1% had adopted an SFP, whereas for clubs with more than 70.5% youth members the prevalence rate was 41.0%. Finally, SFP adoption was higher among sports clubs in the most urbanised municipalities (36.5%) compared with sports clubs in the least urbanised municipalities (15.5%). Figure 1 presents changes in the point prevalence of smokefree sports clubs according to characteristics of sports clubs and the degree of urbanisation. Patterns of variation in SFP adoption according to these characteristics were constant during the entire study period. Field hockey clubs, clubs with many members, clubs with high proportions of youth members and clubs located in the most urbanised municipalities were always more likely to have adopted an outdoor SFP. Table 3 presents the results of the regression analyses of the association of SFP adoption with sports clubs' characteristics and the degree of urbanisation. In the multivariate analyses, korfball and field hockey clubs were significantly more likely to be smoke free compared with football clubs, with respectively an adjusted OR (aOR) of 6.65 (95% CI 4.98 to 8.88) and an aOR of 6.00 (95% CI 4.46 to 8.07), respectively. Clubs with more than 548 members had 8.75 times higher odds (95% CI 6.20 to 12.35) of having an outdoor SFP compared with clubs with 120 members or less. The odds of being smoke-free for clubs with more than 70.5% youth members was 4.22 (95% CI 2.63 to 6.77) compared with clubs with less than 14.5% youth members. The univariate analyses showed a significant association between sports clubs located in the most urbanised municipalities and having an outdoor SFP with an unadjusted OR (uOR) of 3.54 (95% CI 2.19 to 5.70). In the multivariate analyses, this association was still statistically significant but substantially weakened (aOR 1.73, 95% CI 1.01 to 2.96). For all three categorical dependent variables, there was a dose-response relationship with SFP prevalence.

Original research
The density of smoke-free sports clubs within a municipality changed over time (see appendix III). In 2016, only 12 out of 380 municipalities (3.2%) had at least one sports club with an outdoor SFP in their municipality. Between 2016 and 2020, the number of municipalities with at least one smoke-free sports club increased to 77.6%. At the end of 2020, nearly half of all municipalities (49.7%) had over 20% of smoke-free sports clubs within their municipality. Table 4 presents the association between the density of smoke-free sports clubs within a municipality and the annual incidence of an outdoor SFP. In both the adjusted and unadjusted analyses, significant associations were observed for all included years (2018, 2019 and 2020). In 2018, clubs located in a municipality with a relatively high density of smoke-free sports clubs (between 21% and 40% by the end of 2017) had 1.91 higher odds (95% CI 0.31 to 11.76) of adopting an outdoor SFP compared with clubs located in municipalities without smoke-free sports clubs. Similarly, in 2019 and 2020, being a sports club located in a municipality with a higher initial density of smoke-free sports clubs was associated with 2.41 (95% CI 1.51 to 3.85) and 1.63 (95% CI 1.10 to 2.44) higher odds of becoming smoke free, respectively.

Key findings
This study found that by the end of 2020, a quarter of all football, tennis, field hockey and korfball clubs in the Netherlands had adopted an outdoor SFP. Field hockey and korfball clubs, clubs with many members and clubs with high proportions of youth members were more likely to have adopted an outdoor SFP. Outdoor SFPs at sports clubs diffused across the urban hierarchy, from most urbanised to least urbanised municipalities. In addition to hierarchical diffusion, we observed a pattern of horizontal diffusion, as a high density of smoke-free sports clubs appeared to influence the incidence of new adoption within the same municipality the following year.

Interpretation of findings
The large increase in the number of Dutch sports clubs with an outdoor SFP may be attributed to a number of factors. First, in the Netherlands, public support for smoke-free environments increased from 65% in 2014 to 76% in 2019. Moreover, in 2019, 85% of Dutch adults supported smokefree sports clubs. 22 This is related to a changing social norm in the Netherlands with regard to smoking. 12 Second, the NPA of 2018 may have motivated sports federations and municipalities to support sports clubs to become smokefree. Following this agreement, increasingly more municipalities had been formulating local prevention agreements that outlined local strategies to achieve the goals established in the NPA, including smoke-free sports. 23 Finally, a national cooperation of the Dutch Cancer Society, the Dutch Heart Foundation and the Lung Fund has extensively campaigned for smoke-free sports clubs, for example, by broadcasting TV commercials and promoting newspaper articles.
Contrary to the preceding trend, the incidence of smokefree sports clubs declined in 2020. Although this might indicate that the adoption of outdoor SFPs in the Netherlands stagnated, it is more likely that the COVID-19 pandemic played a role, since sports clubs were closed for a large part of the year.
This study found a strong association between the characteristics of sports clubs and the adoption of an outdoor SFP. The difference between field hockey clubs and other types of sports in the adoption of outdoor SFPs could have to do with the higher educational and income level of members of field hockey clubs. Field hockey is generally perceived as an elite sport, in which the higher educated are five times more likely to participate than the lower educated. 24 Given the association between smoking and socioeconomic status, 25 26 field hockey clubs might have experienced fewer barriers to adopt an outdoor SFP, as fewer club members are likely to smoke and to oppose the SFP. 12 Although tennis, like hockey, is considered an elite sport, tennis clubs had the lowest percentage of outdoor SFP adoption. This could be due to the fact that tennis attracts substantially fewer youth members than other type of sports. Support for SFPs has proven to be higher in settings meant for children, primarily since protecting children from exposure to SHS is generally seen as a legitimate reason to introduce SFPs at outdoor environments. [27][28][29] This study found evidence for horizontal diffusion of outdoor SFPs among sports clubs within the same municipality. Similar patterns were reported in an Indonesian study that found that SFP adoption in districts increased when adjacent districts had already adopted an SFP. 16 Within the Netherlands, horizontal diffusion has also been observed for other health-related innovations. For example, in a study on the establishment of Centers for Youth and Family within municipalities, it was found that a municipality was more likely to adopt a centre if other municipalities in the same regional network had already adopted one. 30 Sports clubs might copy nearby smoke-free sports clubs, as the development of a policy is often stimulated by a nearby organisation's successful experience with such a policy. 31 Nykiforuk et al 15 labels this process 'expansion' diffusion, arguing that areas closer to the point of initiation are more likely to adopt a policy in an early stage.
We found that sports clubs in more urban areas were more likely to adopt outdoor SFP, which is in line with a hierarchical diffusion pattern. Similarly, Nykiforuk et al 15 reported hierarchical diffusion patterns regarding the adoption of smoke-free bylaw, although these patterns downward (from larger to smaller cities) and upward (from smaller to larger cities). It is important to note this pattern may not be attributed solely to the degree of urbanisation per se. We found that this effect is largely mediated by sports clubs' characteristics, that is, clubs in more rural municipalities are often smaller clubs. Thus, even though the degree of urbanisation matters, it plays less of a role than characteristics of individual sports clubs.

Strengths and limitations
A strength of our study is that we included all sports clubs with regard to the four most popular outdoor sports among Dutch children. These sports vary in terms of prestige or socioeconomic status and include both individual and team sports. This increases the generalisability of our findings to other type of sports in the Netherlands. The transferability to other countries is uncertain. It would be of interest to conduct the current study in other countries, particularly in countries Table 3 The association between sports club characteristics, degree of urbanisation and the point prevalence of an outdoor SFP by the end of 2020

Original research
with different national organisation and local embedment of sports clubs. This study also has a number of limitations that should be considered when interpreting the results. First, there is currently no mandatory registration of smoke-free sports clubs in the Netherlands. Therefore, sports clubs with an outdoor SFP that did not register with the Dutch Heart Foundation might have been missed. This could have led to an underestimation of the point prevalence and annual incidence of SFPs. However, it is estimated that most sports clubs do register since they receive benefits such as smoke-free signs. A second limitation is the lack of detailed data. For example, we had no data on the comprehensiveness of SFPs at sports club, as there are currently no specific criteria for sports clubs to be registered as smoke free. Therefore, the comprehensiveness of policies can differ between sports clubs, from banning smoking only at certain times, days or places, to banning smoking at all times and on the entire grounds of the sports club.

CONCLUSION AND IMPLICATIONS
Since 2016, the number of Dutch sports clubs with an outdoor SFP has been steadily increasing, with field hockey and korfball clubs, and clubs with many (youth) members taking the lead. Outdoor SFPs at sports clubs diffuse across horizontal and hierarchical lines, although the latter can largely be attributed to diffusion according to club characteristics. In order to ensure that all sports clubs are smoke free by 2025, focus needs to shift towards clubs and municipalities that are less likely to adopt SFPs, such as football and tennis clubs, smaller clubs and clubs in less urbanised areas. Stakeholders such as municipal health services or national sports federations can respond to this challenge in several ways. For example, they can monitor which sports clubs become smoke free, provide extra support to clubs that are less likely to adopt SFPs and gather the positive experiences of spearhead clubs in order to use these to promote SFP adoption among laggards.
Contributors RAS conducted literature searches, analysed the data, and wrote the original draft of the manuscript. HHG and AEK conceptualised the study and reviewed the manuscript. AEK is acting as guarantor. All authors have seen and approved the final version of the manuscript. The manuscript is the authors' original work, has not received prior publication and is not under consideration for publication elsewhere.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.

Patient consent for publication Not applicable.
Ethics approval This study involves human participants, but The Medical Ethics Review Committee of the Academic Medical Center confirmed that the Dutch Medical Research Involving Human Subjects Act (WMO) did not apply to this study and that an official approval was not required (W20_318 # 20.369). Participants gave informed consent to participate in the study before taking part.
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement Data are available on reasonable request.

ORCID iD
Heike H Garritsen http://orcid.org/0000-0003-4491-6814 Table 4 Association between the density of smoke-free sports clubs (by the end of 2017, 2018 and 2019) and the annual incidence of an outdoor SFP within the same municipality (in 2018, 2019 and 2020) *Adjusted models were controlled for variables: type of sport, total number of members, proportion of youth members and degree of urbanisation. †These variables do not contain a 100% category, as the highest percentages of smoke-free sports clubs did not exceed 40% (2017) or 67% (2018). ‡Categories were merged due to small numbers.

What this paper adds
What is already known on this subject ► Smoke-free policies (SFPs) have been associated with smoking cessation, reduced tobacco use, reduced likelihood of smoking initiation among youth and denormalisation of smoking. ► Outdoor SFPs at sports clubs have great potential to reduce the exposure of youth to SHS as sports clubs are often visited by children. ► Policies can have different diffusion patterns, for example, horizontal (following adjacent areas) and hierarchical (following the urban hierarchy).
What important gaps in knowledge exist on this topic ► The diffusion patterns of outdoor SFPs have not been studied before. ► Understanding these diffusion patterns and the characteristics that are associated with the early adoption of such policies may inform national strategies aimed at making all outdoor sports clubs smoke free.
What this paper adds ► Outdoor SFPs at sports clubs in the Netherlands diffused across horizontal and hierarchical lines. ► Hierarchical diffusion could be largely attributed to diffusion according to club characteristics. ► In order to increase adoption of outdoor SFPs at sports clubs, focus needs to shift to clubs and municipalities that are likely to stay behind, such as football and tennis clubs, smaller clubs and clubs in less urbanised areas.